Recently, biometric authentication techniques have been developed to make contactless (or non-contact) authentication of a system user, based on an biometric image representing biometric information such as a vein pattern of a hand or finger, a fingerprint, a palmprint, or the like. A biometric authentication apparatus utilizing the biometric authentication technique collates an input biometric image representing the user's biometric information with registered biometric information representing a biometric image of a registered user registered in advance. In a case in which the input biometric information and the registered biometric information match as a result of the collating process, the biometric authentication apparatus authenticates the user as a legitimate user (that is, the registered user) who is authorized to use the system, and permits the authenticated user to use the system. For example, the biometric authentication apparatus may be built into the system, or may be externally connected to the system.
The biometric authentication apparatus is being utilized in various fields, such as log-on management to a personal computer, identify verification in an ATM (Automated Teller Machine) of a bank, access management to an office, or the like, for example. In addition, the size of the biometric authentication apparatus itself is being reduced in order to expand the range in which the biometric authentication apparatus may be applied.
In order for the biometric authentication apparatus to authenticate the user with a high accuracy, it is desirable that a feature configuration of the biometric information clearly appears on the biometric image. For this reason, a sensor used in the biometric authentication apparatus to generate the biometric image may be provided with an illuminating optical system that irradiates illumination light on a capturing target such as the user's hand, in addition to an imaging optical system that captures the biometric information of the capturing target such as the user's hand using an imaging lens and an imaging device such as a CCD (Charged Coupled Device).
For example, Japanese Laid-Open Patent Publication No. 2004-78791 proposes a biometric authentication technique using the illuminating optical system and the imaging optical system. According to this proposed biometric authentication technique, the illuminating optical system is formed by a plurality of light emitting diodes that are arranged two-dimensionally to a size greater than or equal to a biometric region of the capturing target, in order to irradiate the illumination light on a relatively large biometric region.
On the other hand, Japanese National Publication of International Patent Application No. 2008-537785, for example, proposes an illuminating optical system technique for screen illumination. According to this proposed illuminating optical system, the screen is segmented into predetermined regions, and a number of point light sources corresponding to the number of segmented regions are arranged. In addition, an optical guide element with a surface provided with a diffraction surface element having the same size as the screen is arranged between the point light sources and the screen, in order to convert light from the point light sources into parallel light (or rays) and irradiate the screen with illumination light having a uniform intensity distribution.
However, according to the proposed techniques described above, the size of the illuminating optical system is greater than or equal to an illuminating region that is irradiated by the illumination light, and it is difficult to apply the proposed techniques to the biometric authentication apparatus that is being reduced in size.
Conventionally, it is difficult to irradiate the illumination light with a uniform intensity distribution on the illuminating region that is larger than the illumination device.